Encapsulated electronics

ABSTRACT

An eye-mountable device includes an electrochemical sensor embedded in a polymeric material configured for mounting to a surface of an eye. The electrochemical sensor includes a working electrode and a reference electrode that reacts with an analyte to generate a sensor measurement related to a concentration of the analyte in a fluid to which the eye-mountable device is exposed. An example assembly process includes: forming a sacrificial layer on a working substrate; forming a first layer of a bio-compatible material on the sacrificial layer; providing an electronics module on the first layer of the bio-compatible material, forming a second layer of the bio-compatible material to cover the electronics module; and annealing the first and second layers of the bio-compatible material together to form an encapsulated structure having the electronics module fully encapsulated by the bio-compatible material.

BACKGROUND

Unless otherwise indicated herein, the materials described in thissection are not prior art to the claims in this application and are notadmitted to be prior art by inclusion in this section.

An electrochemical amperometric sensor measures a concentration of ananalyte by measuring a current generated through electrochemicaloxidation or reduction reactions of the analyte at a working electrodeof the sensor. A reduction reaction occurs when electrons aretransferred from the electrode to the analyte, whereas an oxidationreaction occurs when electrons are transferred from the analyte to theelectrode. The direction of the electron transfer is dependent upon theelectrical potentials applied to the working electrode. A counterelectrode and/or reference electrode is used to complete a circuit withthe working electrode and allow the generated current to flow. When theworking electrode is appropriately biased, the output current can beproportional to the reaction rate, so as to provide a measure of theconcentration of the analyte surrounding the working electrode.

In some examples, a reagent is localized proximate the working electrodeto selectively react with a desired analyte. For example, glucoseoxidase can be fixed near the working electrode to react with glucoseand release hydrogen peroxide, which is then electrochemically detectedby the working electrode to indicate the presence of glucose. Otherenzymes and/or reagents can be used to detect other analytes.

SUMMARY

Some embodiments of the present disclosure provide an eye-mountabledevice including a transparent polymeric material, a substrate, anantenna, and a controller. The transparent polymeric material can have aconcave surface and a convex surface. The concave surface can beconfigured to be removably mounted over a corneal surface and the convexsurface can be configured to be compatible with eyelid motion when theconcave surface is so mounted. The substrate can be at least partiallyembedded in the transparent polymeric material. The substrate caninclude an electrochemical sensor that includes a working electrode anda reference electrode. The substrate can also include an electronicsmodule encapsulated within a bio-compatible material such that tearfluid permeating the transparent polymeric material is isolated from theelectronics module by the bio-compatible material. The electronicsmodule can includes an antenna and a controller. The controller can beelectrically connected to the electrochemical sensor and the antenna.The controller can be configured to control the electrochemical sensorto obtain a sensor measurement related to a concentration of an analytein a fluid to which the eye-mountable device is exposed and use theantenna to indicate the sensor measurement.

Some embodiments of the present disclosure provide a method includingforming a sacrificial layer on a working substrate. The method caninclude forming a first layer of a bio-compatible material on thesacrificial layer. The method can include providing an electronicsmodule on the first layer of the bio-compatible material. The method caninclude forming a second layer of the bio-compatible material to coverthe electronics module. The method can include annealing the first andsecond layers of the bio-compatible material together to form anencapsulated structure. The encapsulated structure can include theelectronics module fully enclosed within the bio-compatible material.

Some embodiments of the present disclosure provide a device prepared bya process. The process can include forming a sacrificial layer on aworking substrate. The process can include forming a first layer of abio-compatible material on the sacrificial layer. The process caninclude providing an electronics module on the first layer of thebio-compatible material. The process can include forming a second layerof the bio-compatible material to cover the electronics module. Theprocess can include annealing the first and second layers of thebio-compatible material together to form an encapsulated structure. Theencapsulated structure can include the electronics module fully enclosedwithin the bio-compatible material.

These as well as other aspects, advantages, and alternatives, willbecome apparent to those of ordinary skill in the art by reading thefollowing detailed description, with reference where appropriate to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example system that includes aneye-mountable device in wireless communication with an external reader.

FIG. 2A is a bottom view of an example eye-mountable device.

FIG. 2B is a side view of the example eye-mountable device shown in FIG.2A.

FIG. 2C is a side cross-section view of the example eye-mountable deviceshown in FIGS. 2A and 2B while mounted to a corneal surface of an eye.

FIG. 2D is a side cross-section view enhanced to show the tear filmlayers surrounding the surfaces of the example eye-mountable device whenmounted as shown in FIG. 2C.

FIG. 3 is a functional block diagram of an example system forelectrochemically measuring a tear film analyte concentration.

FIG. 4A is a flowchart of an example process for operating anamperometric sensor in an eye-mountable device to measure a tear filmanalyte concentration.

FIG. 4B is a flowchart of an example process for operating an externalreader to interrogate an amperometric sensor in an eye-mountable deviceto measure a tear film analyte concentration.

FIGS. 5A-5H show stages of fabricating an example structure in which anelectronics module is encapsulated.

FIG. 6A is a flowchart of an example process for fabricating anencapsulated structure.

FIG. 6B is a flowchart of an example process for incorporating anencapsulated structure into an eye-mountable device.

FIG. 7 depicts a computer-readable medium configured according to anexample embodiment.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying figures, which form a part hereof. In the figures, similarsymbols typically identify similar components, unless context dictatesotherwise. The illustrative embodiments described in the detaileddescription, figures, and claims are not meant to be limiting. Otherembodiments may be utilized, and other changes may be made, withoutdeparting from the scope of the subject matter presented herein. It willbe readily understood that the aspects of the present disclosure, asgenerally described herein, and illustrated in the figures, can bearranged, substituted, combined, separated, and designed in a widevariety of different configurations, all of which are explicitlycontemplated herein.

I. Overview

An ophthalmic sensing platform or implantable sensing platform caninclude a sensor, control electronics and an antenna all situated on asubstrate embedded in a polymeric material. The polymeric material canbe incorporated in an ophthalmic device, such as an eye-mountable deviceor an implantable medical device. The control electronics can operatethe sensor to perform readings and can operate the antenna to wirelesslycommunicate the readings from the sensor to an external reader via theantenna.

In some examples, the polymeric material can be in the form of a roundlens with a concave curvature configured to mount to a corneal surfaceof an eye. The substrate can be embedded near the periphery of thepolymeric material to avoid interference with incident light receivedcloser to the central region of the cornea. The sensor can be arrangedon the substrate to face inward, toward the corneal surface, so as togenerate clinically relevant readings from near the surface of thecornea and/or from tear fluid interposed between the contact lens andthe corneal surface. In some examples, the sensor is entirely embeddedwithin the contact lens material. For example, an electrochemical sensorthat includes a working electrode and a reference electrode can beembedded in the lens material and situated such that the sensorelectrodes are less than 10 micrometers from the polymeric surfaceconfigured to mount to the cornea. The sensor can generate an outputsignal indicative of a concentration of an analyte that diffuses throughthe lens material to the sensor electrodes.

The ophthalmic sensing platform can be powered via radiated energyharvested at the sensing platform. Power can be provided by lightenergizing photovoltaic cells included on the sensing platform.Additionally or alternatively, power can be provided by radio frequencyenergy harvested from the antenna. A rectifier and/or regulator can beincorporated with the control electronics to generate a stable DCvoltage to power the sensing platform from the harvested energy. Theantenna can be arranged as a loop of conductive material with leadsconnected to the control electronics. In some embodiments, such a loopantenna can also wirelessly communicate the sensor readings to anexternal reader by modifying the impedance of the loop antenna so as tomodify backscatter radiation from the antenna.

Tear fluid contains a variety of inorganic electrolytes (e.g., Ca²⁺,Mg²⁺, Cl⁻), organic components (e.g., glucose, lactate, proteins,lipids, etc.), and so on that can be used to diagnose health states. Anophthalmic sensing platform configured to measure one or more of theseanalytes can thus provide a convenient non-invasive platform useful indiagnosing and/or monitoring health states. For example, an ophthalmicsensing platform can be configured to sense glucose and can be used bydiabetic individuals to measure/monitor their glucose levels.

In some embodiments of the present disclosure, an electronics module isentirely encapsulated by a bio-compatible material. The encapsulatedelectronics module may then be employed in applications involvingcontact with biological fluids without invoking a host response. Anexample technique for producing such an encapsulated electronics moduleis also disclosed herein. The electronics module can be encapsulated bybuilding up a multi-layered structure, where the outer layers are formedof a bio-compatible material, and an inner layer includes theelectronics module. Once the multi-layered structure is assembled, therespective outer layers of bio-compatible material can be annealedtogether to seal the edges around the electronics module. In someexamples, the multi-layered structure can be assembled on a workingsubstrate, such as a silicon wafer or another substantially flat surfacesuitable to be used as a microfabrication substrate. To prevent adhesionbetween the working substrate and the bio-compatible material during theannealing process, a sacrificial layer can be interposed between theworking substrate and the bio-compatible material. The sacrificial layercan then be rinsed away, dissolved, or otherwise removed to release themulti-layered structure from the working substrate.

An example process for fabricating such a bio-compatible encapsulatedelectronics module is described. A first layer of bio-compatiblematerial is formed by evaporation or another microfabrication technique.An electronics module is then provided on the first layer ofbio-compatible material. A second layer of the bio-compatible materialis then formed over the entire region spanned by the electronics module.Following the deposition of the second layer, the electronics module issituated between the first and second layers of bio-compatible material.For example, the top and bottom of the electronics module can be coveredby the first and second layers of the bio-compatible material,respectively. The first and second layers of the bio-compatible materialare deposited to span a greater coverage area than the electronicsmodule such that areas where the second layer of the bio-compatiblematerial is deposited directly on the first layer of the bio-compatiblematerial surround the side edges of the electronics module.

The first and second layers are annealed together by placing the entiremulti-layered structure in an oven heated to a temperature sufficient toanneal the bio-compatible material. Following the annealing, areas wherethe two layers of bio-compatible materials directly contacted oneanother, including the side edges of the electronics module, are sealedtogether by the annealed bond. The electronic components are therebyfully encapsulated by the bio-compatible material. In an example wherethe bio-compatible material is parylene C (e.g., dichlorodi-p-xylylene),the annealing temperature can be a temperature between 150 and 200degrees Celsius.

In some examples, the layered structure is developed on a flat workingsubstrate, such as a silicon wafer, and the annealing process is carriedout while the layered structure is on the working substrate. Inaddition, a sacrificial layer can be coated on the working substrateprior to the deposition of the first layer of bio-compatible material.The sacrificial layer separates the bio-compatible material from theworking substrate, and thereby prevents the bio-compatible material fromadhering to the working substrate during the annealing process. Thesacrificial layer can be a photoresist and/or a non-stick coating suchas silane, soap, etc. Following the annealing process, the sacrificiallayer may be dissolved by rinsing with a suitable solution to therebyrelease the bio-compatible encapsulated electronics from the workingsubstrate. A rinsing solution may include acetone, isopropyl alcohol,and/or water. Generally, the rinsing solution is selected to dissolvethe sacrificial layer without affecting the bio-compatible material.

In some examples, the layered structure is developed on a workingsubstrate that is not coated with a sacrificial layer. For example, thefirst layer of bio-compatible material can be applied directly on aworking substrate, such as a clean silicon wafer. Electronics to beencapsulated can then be provided on the first layer of bio-compatiblematerial and a second layer of bio-compatible material can be formedover the electronics. Following the annealing, the bio-compatibleencapsulated electronics can be peeled away from the working substrate.In some examples, the bio-compatible material may form a conformalcoating around the working substrate, such as where the layers ofbio-compatible material are formed by an evaporation process. Thebio-compatible encapsulated electronics may be peeled away from theworking substrate after the portions of the bio-compatible material thatwrap around the working substrate are trimmed away (e.g., by etching theannealed layers of bio-compatible material to create an encapsulatedelectronics structure with a desired shape).

In some examples, the layered structure can be formed into a desiredshape following the annealing. For example, where the layered structureis developed on a working substrate, oxygen plasma can be used to etchthe layered structure prior to rinsing the encapsulated electronicsmodule from the working substrate. For example, the layered structurecan be etched to create a ring-shaped structure configured to beembedded around the perimeter of an eye-mountable device made of asuitable polymeric material.

The electronics module can include a power harvesting system forharvesting energy from incident radiation (e.g., a radio frequencyantenna for inductively harvesting energy from incident radio frequencyradiation and/or a photovoltaic cell for harvesting energy from incidentvisible, infrared, and/or ultraviolet light). The encapsulatedelectronics module can thereby be powered wirelessly.

In one example application, an encapsulated bio-interactive electronicsmodule is embedded in an eye-mountable device. The eye-mountable deviceis configured to rest on a corneal surface of an eye. The eye-mountabledevice may be formed of a polymeric material, such as a hydrogelmaterial similar to that employed for ophthalmic contact lenses. Someexamples of bio-interactive electronics that may be included in theeye-mountable device include biosensors for monitoring tear film analyteconcentrations and/or near-eye displays for providing visual cues to thewearer. Thus, the bio-interactive electronics may receive informationfrom the wearer (e.g., a bio-sensor that captures analyte concentrationinformation) and/or convey information to the wearer (e.g., a near-eyedisplay that communicates information to the wearer). Thebio-interactive electronics can be powered by harvested energy and maynot include a significant on-board power supply and/or power storage.For example, the bio-interactive electronics may be powered via anintegrated antenna configured to inductively harvest energy fromincident radio frequency radiation and/or via a photovoltaic cellconfigured to harvest energy from incident light. The bio-interactiveelectronics module is encapsulated (sealed) within a bio-compatiblematerial by two layers of the bio-compatible material annealed togetherto seal the respective overlapping edges. The bio-compatible materialcan be shaped as a flattened ring situated around the periphery of theeye-mountable device so as to avoid interference with light transmissionto the light-receptive pupil near the central portion of the eye whilethe eye-mountable device is mounted over a corneal surface.

Thus, the bio-interactive electronics module may be a sensing platformwith a sensor, control electronics and an antenna all encapsulatedwithin a bio-compatible substrate. In operation, the control electronicsoperate the sensor to perform readings and operate the antenna towirelessly communicate the readings from the sensor to an externalreader via the antenna. In an example where the sensor is anelectrochemical sensor, the control electronics can be configured toapply an operating voltage to the sensor electrodes sufficient togenerate an amperometric current, measure the amperometric current, anduse the antenna to communicate the measured amperometric current to anexternal reader.

II. Example Ophthalmic Electronics Platform

FIG. 1 is a block diagram of a system 100 that includes an eye-mountabledevice 110 in wireless communication with an external reader 180. Theexposed regions of the eye-mountable device 110 are made of a polymericmaterial 120 formed to be contact-mounted to a corneal surface of aneye. A substrate 130 is embedded in the polymeric material 120 toprovide a mounting surface for a power supply 140, a controller 150,bio-interactive electronics 160, and a communication antenna 170. Thebio-interactive electronics 160 are operated by the controller 150. Thepower supply 140 supplies operating voltages to the controller 150and/or the bio-interactive electronics 160. The antenna 170 is operatedby the controller 150 to communicate information to and/or from theeye-mountable device 110. The antenna 170, the controller 150, the powersupply 140, and the bio-interactive electronics 160 can all be situatedon the embedded substrate 130. Because the eye-mountable device 110includes electronics and is configured to be contact-mounted to an eye,it is also referred to herein as an ophthalmic electronics platform.

To facilitate contact-mounting, the polymeric material 120 can have aconcave surface configured to adhere (“mount”) to a moistened cornealsurface (e.g., by capillary forces with a tear film coating the cornealsurface). Additionally or alternatively, the eye-mountable device 110can be adhered by a vacuum force between the corneal surface and thepolymeric material due to the concave curvature. While mounted with theconcave surface against the eye, the outward-facing surface of thepolymeric material 120 can have a convex curvature that is formed to notinterfere with eye-lid motion while the eye-mountable device 110 ismounted to the eye. For example, the polymeric material 120 can be asubstantially transparent curved polymeric disk shaped similarly to acontact lens.

The polymeric material 120 can include one or more biocompatiblematerials, such as those employed for use in contact lenses or otherophthalmic applications involving direct contact with the cornealsurface. The polymeric material 120 can optionally be formed in partfrom such biocompatible materials or can include an outer coating withsuch biocompatible materials. The polymeric material 120 can includematerials configured to moisturize the corneal surface, such ashydrogels and the like. In some embodiments, the polymeric material 120can be a deformable (“non-rigid”) material to enhance wearer comfort. Insome embodiments, the polymeric material 120 can be shaped to provide apredetermined, vision-correcting optical power, such as can be providedby a contact lens.

The substrate 130 includes one or more surfaces suitable for mountingthe bio-interactive electronics 160, the controller 150, the powersupply 140, and the antenna 170. The substrate 130 can be employed bothas a mounting platform for chip-based circuitry (e.g., by flip-chipmounting to connection pads) and/or as a platform for patterningconductive materials (e.g., gold, platinum, palladium, titanium, copper,aluminum, silver, metals, other conductive materials, combinations ofthese, etc.) to create electrodes, interconnects, connection pads,antennae, etc. In some embodiments, substantially transparent conductivematerials (e.g., indium tin oxide) can be patterned on the substrate 130to form circuitry, electrodes, etc. For example, the antenna 170 can beformed by forming a pattern of gold or another conductive material onthe substrate 130 by deposition, photolithography, electroplating, etc.Similarly, interconnects 151, 157 between the controller 150 and thebio-interactive electronics 160, and between the controller 150 and theantenna 170, respectively, can be formed by depositing suitable patternsof conductive materials on the substrate 130. A combination ofmicrofabrication techniques including, without limitation, the use ofphotoresists, masks, deposition techniques, and/or plating techniquescan be employed to pattern materials on the substrate 130. The substrate130 can be a relatively rigid material, such as polyethyleneterephthalate (“PET”) or another material configured to structurallysupport the circuitry and/or chip-based electronics within the polymericmaterial 120. The eye-mountable device 110 can alternatively be arrangedwith a group of unconnected substrates rather than a single substrate.For example, the controller 150 and a bio-sensor or otherbio-interactive electronic component can be mounted to one substrate,while the antenna 170 is mounted to another substrate and the two can beelectrically connected via the interconnects 157.

In some embodiments, the bio-interactive electronics 160 (and thesubstrate 130) can be positioned away from the center of theeye-mountable device 110 and thereby avoid interference with lighttransmission to the central, light-sensitive region of the eye. Forexample, where the eye-mountable device 110 is shaped as aconcave-curved disk, the substrate 130 can be embedded around theperiphery (e.g., near the outer circumference) of the disk. In someembodiments, however, the bio-interactive electronics 160 (and thesubstrate 130) can be positioned in or near the central region of theeye-mountable device 110. Additionally or alternatively, thebio-interactive electronics 160 and/or substrate 130 can besubstantially transparent to incoming visible light to mitigateinterference with light transmission to the eye. Moreover, in someembodiments, the bio-interactive electronics 160 can include a pixelarray 164 that emits and/or transmits light to be received by the eyeaccording to display instructions. Thus, the bio-interactive electronics160 can optionally be positioned in the center of the eye-mountabledevice so as to generate perceivable visual cues to a wearer of theeye-mountable device 110, such as by displaying information (e.g.,characters, symbols, flashing patterns, etc.) on the pixel array 164.

The substrate 130 can be shaped as a flattened ring with a radial widthdimension sufficient to provide a mounting platform for the embeddedelectronics components. The substrate 130 can have a thicknesssufficiently small to allow the substrate 130 to be embedded in thepolymeric material 120 without influencing the profile of theeye-mountable device 110. The substrate 130 can have a thicknesssufficiently large to provide structural stability suitable forsupporting the electronics mounted thereon. For example, the substrate130 can be shaped as a ring with a diameter of about 10 millimeters, aradial width of about 1 millimeter (e.g., an outer radius 1 millimeterlarger than an inner radius), and a thickness of about 50 micrometers.The substrate 130 can optionally be aligned with the curvature of theeye-mounting surface of the eye-mountable device 110 (e.g., convexsurface). For example, the substrate 130 can be shaped along the surfaceof an imaginary cone between two circular segments that define an innerradius and an outer radius. In such an example, the surface of thesubstrate 130 along the surface of the imaginary cone defines aninclined surface that is approximately aligned with the curvature of theeye mounting surface at that radius.

The power supply 140 is configured to harvest ambient energy to powerthe controller 150 and bio-interactive electronics 160. For example, aradio-frequency energy-harvesting antenna 142 can capture energy fromincident radio radiation. Additionally or alternatively, solar cell(s)144 (“photovoltaic cells”) can capture energy from incoming ultraviolet,visible, and/or infrared radiation. Furthermore, an inertial powerscavenging system can be included to capture energy from ambientvibrations. The energy harvesting antenna 142 can optionally be adual-purpose antenna that is also used to communicate information to theexternal reader 180. That is, the functions of the communication antenna170 and the energy harvesting antenna 142 can be accomplished with thesame physical antenna.

A rectifier/regulator 146 can be used to condition the captured energyto a stable DC supply voltage 141 that is supplied to the controller150. For example, the energy harvesting antenna 142 can receive incidentradio frequency radiation. Varying electrical signals on the leads ofthe antenna 142 are output to the rectifier/regulator 146. Therectifier/regulator 146 rectifies the varying electrical signals to a DCvoltage and regulates the rectified DC voltage to a level suitable foroperating the controller 150. Additionally or alternatively, outputvoltage from the solar cell(s) 144 can be regulated to a level suitablefor operating the controller 150. The rectifier/regulator 146 caninclude one or more energy storage devices to mitigate high frequencyvariations in the ambient energy gathering antenna 142 and/or solarcell(s) 144. For example, one or more energy storage devices (e.g., acapacitor, an inductor, etc.) can be connected in parallel across theoutputs of the rectifier 146 to regulate the DC supply voltage 141 andconfigured to function as a low-pass filter.

The controller 150 is turned on when the DC supply voltage 141 isprovided to the controller 150, and the logic in the controller 150operates the bio-interactive electronics 160 and the antenna 170. Thecontroller 150 can include logic circuitry configured to operate thebio-interactive electronics 160 so as to interact with a biologicalenvironment of the eye-mountable device 110. The interaction couldinvolve the use of one or more components, such an analyte bio-sensor162, in bio-interactive electronics 160 to obtain input from thebiological environment. Additionally or alternatively, the interactioncould involve the use of one or more components, such as pixel array164, to provide an output to the biological environment.

In one example, the controller 150 includes a sensor interface module152 that is configured to operate analyte bio-sensor 162. The analytebio-sensor 162 can be, for example, an amperometric electrochemicalsensor that includes a working electrode and a reference electrode. Avoltage can be applied between the working and reference electrodes tocause an analyte to undergo an electrochemical reaction (e.g., areduction and/or oxidation reaction) at the working electrode. Theelectrochemical reaction can generate an amperometric current that canbe measured through the working electrode. The amperometric current canbe dependent on the analyte concentration. Thus, the amount of theamperometric current that is measured through the working electrode canprovide an indication of analyte concentration. In some embodiments, thesensor interface module 152 can be a potentiostat configured to apply avoltage difference between working and reference electrodes whilemeasuring a current through the working electrode.

In some instances, a reagent can also be included to sensitize theelectrochemical sensor to one or more desired analytes. For example, alayer of glucose oxidase (“GOD”) proximal to the working electrode cancatalyze glucose oxidation to generate hydrogen peroxide (H₂O₂). Thehydrogen peroxide can then be electro-oxidized at the working electrode,which releases electrons to the working electrode, resulting in anamperometric current that can be measured through the working electrode.

The current generated by either reduction or oxidation reactions isapproximately proportionate to the reaction rate. Further, the reactionrate is dependent on the rate of analyte molecules reaching theelectrochemical sensor electrodes to fuel the reduction or oxidationreactions, either directly or catalytically through a reagent. In asteady state, where analyte molecules diffuse to the electrochemicalsensor electrodes from a sampled region at approximately the same ratethat additional analyte molecules diffuse to the sampled region fromsurrounding regions, the reaction rate is approximately proportionate tothe concentration of the analyte molecules. The current measured throughthe working electrode thus provides an indication of the analyteconcentration.

The controller 150 can optionally include a display driver module 154for operating a pixel array 164. The pixel array 164 can be an array ofseparately programmable light transmitting, light reflecting, and/orlight emitting pixels arranged in rows and columns. The individual pixelcircuits can optionally include liquid crystal technologies,microelectromechanical technologies, emissive diode technologies, etc.to selectively transmit, reflect, and/or emit light according toinformation from the display driver module 154. Such a pixel array 164can also optionally include more than one color of pixels (e.g., red,green, and blue pixels) to render visual content in color. The displaydriver module 154 can include, for example, one or more data linesproviding programming information to the separately programmed pixels inthe pixel array 164 and one or more addressing lines for setting groupsof pixels to receive such programming information. Such a pixel array164 situated on the eye can also include one or more lenses to directlight from the pixel array to a focal plane perceivable by the eye.

The controller 150 can also include a communication circuit 156 forsending and/or receiving information via the antenna 170. Thecommunication circuit 156 can optionally include one or moreoscillators, mixers, frequency injectors, etc. to modulate and/ordemodulate information on a carrier frequency to be transmitted and/orreceived by the antenna 170. In some examples, the eye-mountable device110 is configured to indicate an output from a bio-sensor by modulatingan impedance of the antenna 170 in a manner that is perceivable by theexternal reader 180. For example, the communication circuit 156 cancause variations in the amplitude, phase, and/or frequency ofbackscatter radiation from the antenna 170, and such variations can bedetected by the reader 180.

The controller 150 is connected to the bio-interactive electronics 160via interconnects 151. For example, where the controller 150 includeslogic elements implemented in an integrated circuit to form the sensorinterface module 152 and/or display driver module 154, a patternedconductive material (e.g., gold, platinum, palladium, titanium, copper,aluminum, silver, metals, combinations of these, etc.) can connect aterminal on the chip to the bio-interactive electronics 160. Similarly,the controller 150 is connected to the antenna 170 via interconnects157.

It is noted that the block diagram shown in FIG. 1 is described inconnection with functional modules for convenience in description.However, embodiments of the eye-mountable device 110 can be arrangedwith one or more of the functional modules (“sub-systems”) implementedin a single chip, integrated circuit, and/or physical component. Forexample, while the rectifier/regulator 146 is illustrated in the powersupply block 140, the rectifier/regulator 146 can be implemented in achip that also includes the logic elements of the controller 150 and/orother features of the embedded electronics in the eye-mountable device110. Thus, the DC supply voltage 141 that is provided to the controller150 from the power supply 140 can be a supply voltage that is providedto components on a chip by rectifier and/or regulator components locatedon the same chip. That is, the functional blocks in FIG. 1 shown as thepower supply block 140 and controller block 150 need not be implementedas physically separated modules. Moreover, one or more of the functionalmodules described in FIG. 1 can be implemented by separately packagedchips electrically connected to one another.

Additionally or alternatively, the energy harvesting antenna 142 and thecommunication antenna 170 can be implemented with the same physicalantenna. For example, a loop antenna can both harvest incident radiationfor power generation and communicate information via backscatterradiation.

The external reader 180 includes an antenna 188 (or group of more thanone antennae) to send and receive wireless signals 171 to and from theeye-mountable device 110. The external reader 180 also includes acomputing system with a processor 186 in communication with a memory182. The memory 182 is a non-transitory computer-readable medium thatcan include, without limitation, magnetic disks, optical disks, organicmemory, and/or any other volatile (e.g. RAM) or non-volatile (e.g. ROM)storage system readable by the processor 186. The memory 182 can includea data storage 183 to store indications of data, such as sensor readings(e.g., from the analyte bio-sensor 162), program settings (e.g., toadjust behavior of the eye-mountable device 110 and/or external reader180), etc. The memory 182 can also include program instructions 184 forexecution by the processor 186 to cause the external reader 180 toperform processes specified by the instructions 184. For example, theprogram instructions 184 can cause external reader 180 to provide a userinterface that allows for retrieving information communicated from theeye-mountable device 110 (e.g., sensor outputs from the analytebio-sensor 162). The external reader 180 can also include one or morehardware components for operating the antenna 188 to send and receivethe wireless signals 171 to and from the eye-mountable device 110. Forexample, oscillators, frequency injectors, encoders, decoders,amplifiers, filters, etc. can drive the antenna 188 according toinstructions from the processor 186.

The external reader 180 can be a smart phone, digital assistant, orother portable computing device with wireless connectivity sufficient toprovide the wireless communication link 171. The external reader 180 canalso be implemented as an antenna module that can be plugged in to aportable computing device, such as in an example where the communicationlink 171 operates at carrier frequencies not commonly employed inportable computing devices. In some instances, the external reader 180is a special-purpose device configured to be worn relatively near awearer's eye to allow the wireless communication link 171 to operatewith a low power budget. For example, the external reader 180 can beintegrated in a piece of jewelry such as a necklace, earing, etc. orintegrated in an article of clothing worn near the head, such as a hat,headband, etc.

In an example where the eye-mountable device 110 includes an analytebio-sensor 162, the system 100 can be operated to monitor the analyteconcentration in tear film on the surface of the eye. Thus, theeye-mountable device 110 can be configured as a platform for anophthalmic analyte bio-sensor. The tear film is an aqueous layersecreted from the lacrimal gland to coat the eye. The tear film is incontact with the blood supply through capillaries in the structure ofthe eye and includes many biomarkers found in blood that are analyzed tocharacterize a person's health condition(s). For example, the tear filmincludes glucose, calcium, sodium, cholesterol, potassium, otherbiomarkers, etc. The biomarker concentrations in the tear film can besystematically different than the corresponding concentrations of thebiomarkers in the blood, but a relationship between the twoconcentration levels can be established to map tear film biomarkerconcentration values to blood concentration levels. For example, thetear film concentration of glucose can be established (e.g., empiricallydetermined) to be approximately one tenth the corresponding bloodglucose concentration. Although another ratio relationship and/or anon-ratio relationship may be used. Thus, measuring tear film analyteconcentration levels provides a non-invasive technique for monitoringbiomarker levels in comparison to blood sampling techniques performed bylancing a volume of blood to be analyzed outside a person's body.Moreover, the ophthalmic analyte bio-sensor platform disclosed here canbe operated substantially continuously to enable real time monitoring ofanalyte concentrations.

To perform a reading with the system 100 configured as a tear filmanalyte monitor, the external reader 180 can emit radio frequencyradiation 171 that is harvested to power the eye-mountable device 110via the power supply 140. Radio frequency electrical signals captured bythe energy harvesting antenna 142 (and/or the communication antenna 170)are rectified and/or regulated in the rectifier/regulator 146 and aregulated DC supply voltage 147 is provided to the controller 150. Theradio frequency radiation 171 thus turns on the electronic componentswithin the eye-mountable device 110. Once turned on, the controller 150operates the analyte bio-sensor 162 to measure an analyte concentrationlevel. For example, the sensor interface module 152 can apply a voltagebetween a working electrode and a reference electrode in the analytebio-sensor 162. The applied voltage can be sufficient to cause theanalyte to undergo an electrochemical reaction at the working electrodeand thereby generate an amperometric current that can be measuredthrough the working electrode. The measured amperometric current canprovide the sensor reading (“result”) indicative of the analyteconcentration. The controller 150 can operate the antenna 170 tocommunicate the sensor reading back to the external reader 180 (e.g.,via the communication circuit 156). The sensor reading can becommunicated by, for example, modulating an impedance of thecommunication antenna 170 such that the modulation in impedance isdetected by the external reader 180. The modulation in antenna impedancecan be detected by, for example, backscatter radiation from the antenna170.

In some embodiments, the system 100 can operate to non-continuously(“intermittently”) supply energy to the eye-mountable device 110 topower the controller 150 and electronics 160. For example, radiofrequency radiation 171 can be supplied to power the eye-mountabledevice 110 long enough to carry out a tear film analyte concentrationmeasurement and communicate the results. For example, the supplied radiofrequency radiation can provide sufficient power to apply a potentialbetween a working electrode and a reference electrode sufficient toinduce electrochemical reactions at the working electrode, measure theresulting amperometric current, and modulate the antenna impedance toadjust the backscatter radiation in a manner indicative of the measuredamperometric current. In such an example, the supplied radio frequencyradiation 171 can be considered an interrogation signal from theexternal reader 180 to the eye-mountable device 110 to request ameasurement. By periodically interrogating the eye-mountable device 110(e.g., by supplying radio frequency radiation 171 to temporarily turnthe device on) and storing the sensor results (e.g., via the datastorage 183), the external reader 180 can accumulate a set of analyteconcentration measurements over time without continuously powering theeye-mountable device 110.

FIG. 2A is a bottom view of an example eye-mountable electronic device210 (or ophthalmic electronics platform). FIG. 2B is an aspect view ofthe example eye-mountable electronic device shown in FIG. 2A. It isnoted that relative dimensions in FIGS. 2A and 2B are not necessarily toscale, but have been rendered for purposes of explanation only indescribing the arrangement of the example eye-mountable electronicdevice 210. The eye-mountable device 210 is formed of a polymericmaterial 220 shaped as a curved disk. The polymeric material 220 can bea substantially transparent material to allow incident light to betransmitted to the eye while the eye-mountable device 210 is mounted tothe eye. The polymeric material 220 can be a biocompatible materialsimilar to those employed to form vision correction and/or cosmeticcontact lenses in optometry, such as polyethylene terephthalate (“PET”),polymethyl methacrylate (“PMMA”), polyhydroxyethylmethacrylate(“polyHEMA”), silicone hydrogels, combinations of these, etc. Thepolymeric material 220 can be formed with one side having a concavesurface 226 suitable to fit over a corneal surface of an eye. Theopposite side of the disk can have a convex surface 224 that does notinterfere with eyelid motion while the eye-mountable device 210 ismounted to the eye. A circular outer side edge 228 connects the concavesurface 224 and convex surface 226.

The eye-mountable device 210 can have dimensions similar to a visioncorrection and/or cosmetic contact lenses, such as a diameter ofapproximately 1 centimeter, and a thickness of about 0.1 to about 0.5millimeters. However, the diameter and thickness values are provided forexplanatory purposes only. In some embodiments, the dimensions of theeye-mountable device 210 can be selected according to the size and/orshape of the corneal surface of the wearer's eye.

The polymeric material 220 can be formed with a curved shape in avariety of ways. For example, techniques similar to those employed toform vision-correction contact lenses, such as heat molding, injectionmolding, spin casting, etc. can be employed to form the polymericmaterial 220. While the eye-mountable device 210 is mounted in an eye,the convex surface 224 faces outward to the ambient environment whilethe concave surface 226 faces inward, toward the corneal surface. Theconvex surface 224 can therefore be considered an outer, top surface ofthe eye-mountable device 210 whereas the concave surface 226 can beconsidered an inner, bottom surface. The “bottom” view shown in FIG. 2Ais facing the concave surface 226. From the bottom view shown in FIG.2A, the outer periphery 222, near the outer circumference of the curveddisk is curved to extend out of the page, whereas the central region221, near the center of the disk is curved to extend into the page.

A substrate 230 is embedded in the polymeric material 220. The substrate230 can be embedded to be situated along the outer periphery 222 of thepolymeric material 220, away from the central region 221. The substrate230 does not interfere with vision because it is too close to the eye tobe in focus and is positioned away from the central region 221 whereincident light is transmitted to the eye-sensing portions of the eye.Moreover, the substrate 230 can be formed of a transparent material tofurther mitigate effects on visual perception.

The substrate 230 can be shaped as a flat, circular ring (e.g., a diskwith a centered hole). The flat surface of the substrate 230 (e.g.,along the radial width) is a platform for mounting electronics such aschips (e.g., via flip-chip mounting) and for patterning conductivematerials (e.g., via microfabrication techniques such asphotolithography, deposition, plating, etc.) to form electrodes,antenna(e), and/or interconnections. The substrate 230 and the polymericmaterial 220 can be approximately cylindrically symmetric about a commoncentral axis. The substrate 230 can have, for example, a diameter ofabout 10 millimeters, a radial width of about 1 millimeter (e.g., anouter radius 1 millimeter greater than an inner radius), and a thicknessof about 50 micrometers. However, these dimensions are provided forexample purposes only, and in no way limit the present disclosure. Thesubstrate 230 can be implemented in a variety of different form factors,similar to the discussion of the substrate 130 in connection with FIG. 1above.

A loop antenna 270, controller 250, and bio-interactive electronics 260are disposed on the embedded substrate 230. The controller 250 can be achip including logic elements configured to operate the bio-interactiveelectronics 260 and the loop antenna 270. The controller 250 iselectrically connected to the loop antenna 270 by interconnects 257 alsosituated on the substrate 230. Similarly, the controller 250 iselectrically connected to the bio-interactive electronics 260 by aninterconnect 251. The interconnects 251, 257, the loop antenna 270, andany conductive electrodes (e.g., for an electrochemical analytebio-sensor, etc.) can be formed from conductive materials patterned onthe substrate 230 by a process for precisely patterning such materials,such as deposition, photolithography, etc. The conductive materialspatterned on the substrate 230 can be, for example, gold, platinum,palladium, titanium, carbon, aluminum, copper, silver, silver-chloride,conductors formed from noble materials, metals, combinations of these,etc.

As shown in FIG. 2A, which is a view facing the concave surface 226 ofthe eye-mountable device 210, the bio-interactive electronics module 260is mounted to a side of the substrate 230 facing the concave surface226. Where the bio-interactive electronics module 260 includes ananalyte bio-sensor, for example, mounting such a bio-sensor on thesubstrate 230 to be close to the concave surface 226 allows thebio-sensor to sense analyte concentrations in tear film near the surfaceof the eye. However, the electronics, electrodes, etc. situated on thesubstrate 230 can be mounted to either the “inward” facing side (e.g.,situated closest to the concave surface 226) or the “outward” facingside (e.g., situated closest to the convex surface 224). Moreover, insome embodiments, some electronic components can be mounted on one sideof the substrate 230, while other electronic components are mounted tothe opposing side, and connections between the two can be made throughconductive materials passing through the substrate 230.

The loop antenna 270 is a layer of conductive material patterned alongthe flat surface of the substrate to form a flat conductive ring. Insome instances, the loop antenna 270 can be formed without making acomplete loop. For instances, the antenna 270 can have a cutout to allowroom for the controller 250 and bio-interactive electronics 260, asillustrated in FIG. 2A. However, the loop antenna 270 can also bearranged as a continuous strip of conductive material that wrapsentirely around the flat surface of the substrate 230 one or more times.For example, a strip of conductive material with multiple windings canbe patterned on the side of the substrate 230 opposite the controller250 and bio-interactive electronics 260. Interconnects between the endsof such a wound antenna (e.g., the antenna leads) can then be passedthrough the substrate 230 to the controller 250.

FIG. 2C is a side cross-section view of the example eye-mountableelectronic device 210 while mounted to a corneal surface 22 of an eye10. FIG. 2D is a close-in side cross-section view enhanced to show thetear film layers 40, 42 surrounding the exposed surfaces 224, 226 of theexample eye-mountable device 210. It is noted that relative dimensionsin FIGS. 2C and 2D are not necessarily to scale, but have been renderedfor purposes of explanation only in describing the arrangement of theexample eye-mountable electronic device 210. For example, the totalthickness of the eye-mountable device can be about 200 micrometers,while the thickness of the tear film layers 40, 42 can each be about 10micrometers, although this ratio may not be reflected in the drawings.Some aspects are exaggerated to allow for illustration and facilitateexplanation.

The eye 10 includes a cornea 20 that is covered by bringing the uppereyelid 30 and lower eyelid 32 together over the top of the eye 10.Incident light is received by the eye 10 through the cornea 20, wherelight is optically directed to light sensing elements of the eye 10(e.g., rods and cones, etc.) to stimulate visual perception. The motionof the eyelids 30, 32 distributes a tear film across the exposed cornealsurface 22 of the eye 10. The tear film is an aqueous solution secretedby the lacrimal gland to protect and lubricate the eye 10. When theeye-mountable device 210 is mounted in the eye 10, the tear film coatsboth the concave and convex surfaces 224, 226 with an inner layer 40(along the concave surface 226) and an outer layer 42 (along the convexlayer 224). The tear film layers 40, 42 can be about 10 micrometers inthickness and together account for about 10 microliters.

The tear film layers 40, 42 are distributed across the corneal surface22 and/or the convex surface 224 by motion of the eyelids 30, 32. Forexample, the eyelids 30, 32 raise and lower, respectively, to spread asmall volume of tear film across the corneal surface 22 and/or theconvex surface 224 of the eye-mountable device 210. The tear film layer40 on the corneal surface 22 also facilitates mounting the eye-mountabledevice 210 by capillary forces between the concave surface 226 and thecorneal surface 22. In some embodiments, the eye-mountable device 210can also be held over the eye in part by vacuum forces against cornealsurface 22 due to the concave curvature of the eye-facing concavesurface 226.

As shown in the cross-sectional views in FIGS. 2C and 2D, the substrate230 can be inclined such that the flat mounting surfaces of thesubstrate 230 are approximately parallel to the adjacent portion of theconcave surface 226. As described above, the substrate 230 is aflattened ring with an inward-facing surface 232 (closer to the concavesurface 226 of the polymeric material 220) and an outward-facing surface234 (closer to the convex surface 224). The substrate 230 can haveelectronic components and/or patterned conductive materials mounted toeither or both mounting surfaces 232, 234. As shown in FIG. 2D, thebio-interactive electronics 260, controller 250, and conductiveinterconnect 251 are mounted on the inward-facing surface 232 such thatthe bio-interactive electronics 260 are relatively closer in proximityto the corneal surface 22 than if they were mounted on theoutward-facing surface 234.

III. An Ophthalmic Electrochemical Analyte Sensor

FIG. 3 is a functional block diagram of a system 300 forelectrochemically measuring a tear film analyte concentration. Thesystem 300 includes an eye-mountable device 310 with embedded electroniccomponents powered by an external reader 340. The eye-mountable device310 includes an antenna 312 for capturing radio frequency radiation 341from the external reader 340. The eye-mountable device 310 includes arectifier 314, an energy storage 316, and regulator 318 for generatingpower supply voltages 330, 332 to operate the embedded electronics. Theeye-mountable device 310 includes an electrochemical sensor 320 with aworking electrode 322 and a reference electrode 323 driven by a sensorinterface 321. The eye-mountable device 310 includes hardware logic 324for communicating results from the sensor 320 to the external reader 340by modulating the impedance of the antenna 312. An impedance modulator325 (shown symbolically as a switch in FIG. 3) can be used to modulatethe antenna impedance according to instructions from the hardware logic324. Similar to the eye-mountable devices 110, 210 discussed above inconnection with FIGS. 1 and 2, the eye-mountable device 310 can includea mounting substrate embedded within a polymeric material configured tobe mounted to an eye.

The electrochemical sensor 320 can be situated on a mounting surface ofsuch a substrate proximate the surface of the eye (e.g., correspondingto the bio-interactive electronics 260 on the inward-facing side 232 ofthe substrate 230) to measure analyte concentration in a tear film layerinterposed between the eye-mountable device 310 and the eye (e.g., theinner tear film layer 40 between the eye-mountable device 210 and thecorneal surface 22). In some embodiments, however, an electrochemicalsensor can be situated on a mounting surface of such a substrate distalthe surface of the eye (e.g., corresponding to the outward-facing side234 of the substrate 230) to measure analyte concentration in a tearfilm layer coating the exposed surface of the eye-mountable device 310(e.g., the outer tear film layer 42 interposed between the convexsurface 224 of the polymeric material 210 and the atmosphere and/orclosed eyelids).

With reference to FIG. 3, the electrochemical sensor 320 measuresanalyte concentration by applying a voltage between the electrodes 322,323 that is sufficient to cause products of the analyte catalyzed by thereagent to electrochemically react (e.g., a reduction and/or oxidizationreaction) at the working electrode 322. The electrochemical reactions atthe working electrode 322 generate an amperometric current that can bemeasured at the working electrode 322. The sensor interface 321 can, forexample, apply a reduction voltage between the working electrode 322 andthe reference electrode 323 to reduce products from thereagent-catalyzed analyte at the working electrode 322. Additionally oralternatively, the sensor interface 321 can apply an oxidization voltagebetween the working electrode 322 and the reference electrode 323 tooxidize the products from the reagent-catalyzed analyte at the workingelectrode 322. The sensor interface 321 measures the amperometriccurrent and provides an output to the hardware logic 324. The sensorinterface 321 can include, for example, a potentiostat connected to bothelectrodes 322, 323 to simultaneously apply a voltage between theworking electrode 322 and the reference electrode 323 and measure theresulting amperometric current through the working electrode 322.

The rectifier 314, energy storage 316, and voltage regulator 318 operateto harvest energy from received radio frequency radiation 341. The radiofrequency radiation 341 causes radio frequency electrical signals onleads of the antenna 312. The rectifier 314 is connected to the antennaleads and converts the radio frequency electrical signals to a DCvoltage. The energy storage 316 (e.g., capacitor) is connected acrossthe output of the rectifier 314 to filter out high frequency componentsof the DC voltage. The regulator 318 receives the filtered DC voltageand outputs both a digital supply voltage 330 to operate the hardwarelogic 324 and an analog supply voltage 332 to operate theelectrochemical sensor 320. For example, the analog supply voltage canbe a voltage used by the sensor interface 321 to apply a voltage betweenthe sensor electrodes 322, 323 to generate an amperometric current. Thedigital supply voltage 330 can be a voltage suitable for driving digitallogic circuitry, such as approximately 1.2 volts, approximately 3 volts,etc. Reception of the radio frequency radiation 341 from the externalreader 340 (or another source, such as ambient radiation, etc.) causesthe supply voltages 330, 332 to be supplied to the sensor 320 andhardware logic 324. While powered, the sensor 320 and hardware logic 324are configured to generate and measure an amperometric current andcommunicate the results.

The sensor results can be communicated back to the external reader 340via backscatter radiation 343 from the antenna 312. The hardware logic324 receives the output current from the electrochemical sensor 320 andmodulates (325) the impedance of the antenna 312 in accordance with theamperometric current measured by the sensor 320. The antenna impedanceand/or change in antenna impedance is detected by the external reader340 via the backscatter signal 343. The external reader 340 can includean antenna front end 342 and logic components 344 to decode theinformation indicated by the backscatter signal 343 and provide digitalinputs to a processing system 346. The external reader 340 associatesthe backscatter signal 343 with the sensor result (e.g., via theprocessing system 346 according to a pre-programmed relationshipassociating impedance of the antenna 312 with output from the sensor320). The processing system 346 can then store the indicated sensorresults (e.g., tear film analyte concentration values) in a local memoryand/or an external memory (e.g., by communicating with the externalmemory through a network).

In some embodiments, one or more of the features shown as separatefunctional blocks can be implemented (“packaged”) on a single chip. Forexample, the eye-mountable device 310 can be implemented with therectifier 314, energy storage 316, voltage regulator 318, sensorinterface 321, and the hardware logic 324 packaged together in a singlechip or controller module. Such a controller can have interconnects(“leads”) connected to the loop antenna 312 and the sensor electrodes322, 323. Such a controller operates to harvest energy received at theloop antenna 312, apply a voltage between the electrodes 322, 323sufficient to develop an amperometric current, measure the amperometriccurrent, and indicate the measured current via the antenna 312 (e.g.,through the backscatter radiation 343).

FIG. 4A is a flowchart of a process 400 for operating an amperometricsensor in an eye-mountable device to measure a tear film analyteconcentration. Radio frequency radiation is received at an antenna in aneye-mountable device including an embedded electrochemical sensor (402).Electrical signals due to the received radiation are rectified andregulated to power the electrochemical sensor and associated controller(404). For example, a rectifier and/or regulator can be connected to theantenna leads to output a DC supply voltage for powering theelectrochemical sensor and/or controller. A voltage sufficient to causeelectrochemical reactions at the working electrode is applied between aworking electrode and a reference electrode on the electrochemicalsensor (406). An amperometric current is measured through the workingelectrode (408). For example, a potentiostat can apply a voltage betweenthe working and reference electrodes while measuring the resultingamperometric current through the working electrode. The measuredamperometric current is wirelessly indicated with the antenna (410). Forexample, backscatter radiation can be manipulated to indicate the sensorresult by modulating the antenna impedance.

FIG. 4B is a flowchart of a process 420 for operating an external readerto interrogate an amperometric sensor in an eye-mountable device tomeasure a tear film analyte concentration. Radio frequency radiation istransmitted to an electrochemical sensor mounted in an eye from theexternal reader (422). The transmitted radiation is sufficient to powerthe electrochemical sensor with energy from the radiation for longenough to perform a measurement and communicate the results (422). Forexample, the radio frequency radiation used to power the electrochemicalsensor can be similar to the radiation 341 transmitted from the externalreader 340 to the eye-mountable device 310 described in connection withFIG. 3 above. The external reader then receives backscatter radiationindicating the measurement by the electrochemical analyte sensor (424).For example, the backscatter radiation can be similar to the backscattersignals 343 sent from the eye-mountable device 310 to the externalreader 340 described in connection with FIG. 3 above. The backscatterradiation received at the external reader is then associated with a tearfilm analyte concentration (426). In some cases, the analyteconcentration values can be stored in the external reader memory (e.g.,in the processing system 346) and/or a network-connected data storage.

For example, the sensor result (e.g., the measured amperometric current)can be encoded in the backscatter radiation by modulating the impedanceof the backscattering antenna. The external reader can detect theantenna impedance and/or change in antenna impedance based on afrequency, amplitude, and/or phase shift in the backscatter radiation.The sensor result can then be extracted by associating the impedancevalue with the sensor result by reversing the encoding routine employedwithin the eye-mountable device. Thus, the reader can map a detectedantenna impedance value to an amperometric current value. Theamperometric current value is approximately proportionate to the tearfilm analyte concentration with a sensitivity (e.g., scaling factor)relating the amperometric current and the associated tear film analyteconcentration. The sensitivity value can be determined in part accordingto empirically derived calibration factors, for example.

IV. Assembly of an Example Bio-compatible Encapsulated Structure

FIGS. 5A-5H illustrate stages in a process to encapsulate electronics ina bio-compatible material. The illustrations shown in FIG. 5A-5H aregenerally shown in cross-sectional views to illustrate sequentiallyformed layers developed to create a bio-compatible structure thatencapsulates electronics. The layers can be developed bymicrofabrication and/or manufacturing techniques such as, for example,electroplating, photolithography, deposition, and/or evaporationfabrication processes and the like. The various materials may be formedaccording to patterns using photoresists and/or masks to patternmaterials in particular arrangements, such as to form wires, electrodes,connection pads, etc. Additionally, electroplating techniques may alsobe employed to coat an arrangement of electrodes with a metallicplating. For example, an arrangement of conductive material formed by adeposition and/or photolithography process can be plated with a metallicmaterial to create a conductive structure with a desired thickness.However, the dimensions, including relative thicknesses, of the variouslayers illustrated and described in connection with FIGS. 5A-5H tocreate an encapsulated electronics structure are not illustrated toscale. Instead, the drawings in FIGS. 5A-5H schematically illustrate theordering of the various layers for purposes of explanation only.

FIG. 5A illustrates a working substrate 502 coated with a sacrificiallayer 510. The working substrate 502 can be flat surface used toassemble the layers of the encapsulated electronics structure. Forexample, the working substrate 502 can be a wafer (e.g., a siliconwafer) similar to those used in the fabrication of semiconductor deviceand/or microelectronics. The working substrate 502 may be asemiconductive material arranged in a crystalline structure (e.g.,silicon). The working substrate 502 can generally be a substantiallyflat material suitable for receiving layers of material by deposition,photolithography, etc. For example, the working substrate 502 may be asilicon wafer with a polished surface. The sacrificial layer 510 can bea material that adheres to the working substrate 502 and provides asurface on which the encapsulated electronics structure can be formed.As discussed further below, during manufacture of the encapsulatedelectronics structure, the sacrificial layer 510 remains in place untilthe encapsulated electronics structure is fully formed, and then thesacrificial layer 510 is dissolved and/or rinsed by a rinsing agent torelease the encapsulated electronics structure from the workingsubstrate 502. The sacrificial layer 510 thus temporarily attaches theencapsulated electronics structure to the working substrate 502 duringassembly, but releases the completed encapsulated electronics structurefrom the working substrate once assembled.

In some examples, the sacrificial layer 510 can be a positive ornegative photoresist or a non-stick coating. The sacrificial layer 510may include, for example, a silane (e.g., SiH₄), a soap, etc. Thesacrificial layer 510 can be deposited onto the working substrate with asubstantially uniform thickness such that the surface of the sacrificiallayer 510 opposite the working substrate 502 forms a flat surface fordeveloping the encapsulated electronics structure.

FIG. 5B illustrates a first layer of bio-compatible material 520 formedover the sacrificial layer 510. The first layer of the bio-compatiblematerial 520 can be formed by vapor deposition and can have a thicknessof about 1 to about 20 micrometers, for example. The first layer ofbio-compatible material 520 forms a first exterior surface of theencapsulated electronics structure, once the structure is fullyassembled and released from the working substrate 502.

Biocompatibility refers generally to the ability of a material or deviceto co-exist with a biological host. In particular, biocompatiblematerials are generally those that do not bring about a host response(such as an immune response) that result in deleterious effects toeither the biological host or the material. Biocompatible materials aretherefore used in implantable medical devices and/or surgicalinstrumentation, because such materials can be situated within the bodywithout causing toxic or injurious effects. Biocompatible materials arealso used in objects designed to contact tear film covering the eyes,such as contact lens materials. The bio-compatible material can be apolymeric material including parylene, such as parylene C (e.g.,dichlorodi-p-xylylene). Other polymeric materials can also be used,alone or in combination, to form the layer of bio-compatible material520, such as polyethleye terephthalate (PET), polydimethylsiloxane(PDMS) and other silicone elastomers, etc. By selecting a material thatis bio-compatible for the first layer 520, the exterior of theencapsulated electronics structure is able to exist within a biologicalhost. In addition to being bio-compatible, the first layer ofbio-compatible material 520 may be an electrically insulating materialto isolate the encapsulated electronics from the surrounding environment(e.g., from current-carrying particles and/or fluids).

Furthermore, the electronics to be encapsulated may be assembleddirectly on the side of the first layer of bio-compatible material 520opposite the sacrificial layer 510 (i.e., the side of the bio-compatiblematerial that is exposed after forming the first layer of bio-compatiblematerial 520 on the sacrificial layer 510). Thus, the first layer ofbio-compatible material 520 can be a substrate for forming electronics.The bio-compatible material can therefore be a material with sufficientstructural rigidity to be used as a substrate for assembling electronicsby microfabrication processes such as photolithography, etc. However insome embodiments, an additional electronics-assembly substrate can beinterposed between the first layer of bio-compatible material 520 andthe electronics to be encapsulated. However, the total thickness of theassembled structure can be reduced by using the bio-compatible materialitself (e.g., the layer 520) as the electronics assembly surface andthereby avoid inserting an additional layer in the fully assembledstructure.

FIG. 5C illustrates an arrangement of conductive material patterned onthe first layer of bio-compatible material 520 to form electronicscircuitry. The conductive material can be a metal such as platinum,silver, gold, palladium, titanium, copper, chromium, nickel, aluminum,other metals or conductive materials, combinations of these, etc. Someembodiments may employ a substantially transparent conductive materialfor at least some of the electronics circuitry (e.g., a material such asindium tin oxide). The conductive material is patterned to form wires,electrodes, connection pads, etc., for the circuitry of the embeddedelectronics created on the layer of bio-compatible material 520. Theconductive material can be patterned via photolithography, deposition,and/or electroplating, etc. The pattern can then be electricallyconnected to additional circuit components, such as chips, to create abio-interactive electronics module.

For example, metal can be patterned to create components for anelectrochemical bio-sensor circuit powered by harvested radio frequencyenergy, similar to the example electrochemical sensor described above inconnection with FIG. 3. In such an example, the metal can be pattered toform sensor electrodes 530, chip-connection pads 538, 539, an antenna536, and interconnects 532, 534. The sensor electrodes 530 may beelectrodes for an electrochemical sensor, for example, similar to thesensor electrodes 322, 323 discussed in connection with FIG. 3 above.The sensor electrodes 530 may include, for example, a referenceelectrode and a working electrode formed of conductive materials, suchas palladium, platinum, titanium, silver, silver-chloride, gold,aluminum, carbon, combinations of these, etc. The sensor electrodes 530can be arranged in a variety of form factors, such as parallel bars,concentric rings, etc. The working electrode 530 may be amicroelectrode, and may have at least one dimension less than 25micrometers. In one example, the sensor electrodes 530 can be fabricatedby patterning a photoresist in a desired arrangement and thenevaporating metal to create the sensor electrodes 530 according to thepattern of the photoresist.

The antenna 536 can be a loop antenna suitable for receiving radiofrequency radiation harvested to provide a power supply to theelectronics. The antenna 536 may be, for example, a loop with a radiusof approximately 5 millimeters that is suitable for being arrangedaround the perimeter of an eye-mountable device, similar to the antennaillustrated and described in connection with FIGS. 2 and 3 above. Insome instances, the antenna 536 and/or interconnects 532, 534 can beformed of a metal different from metal used in the sensor electrodes 530(e.g., the sensor electrodes 530 may be formed of platinum and theantenna 536 may be formed of gold). The sensor electrodes 530,interconnects 532, 534, and the antenna 536 can be formed with athickness of about 5 micrometers, for example.

The interconnects 532, 534 can be wires formed by photolithography,evaporation, and/or electroplating to connect the sensor electrodes 530to the chip-connection pad 539. The interconnect 532 provides a lowresistance electrical connection between the sensor electrodes 530 andthe electrical components within chip 540 (which is shown and describedin connection with FIG. 5D). Moreover, while the interconnect 532 isshown schematically as a single wire, multiple interconnects may be usedto connect each of a plurality of sensor electrodes to electricalcomponents within chip 540 (e.g., components that function similarly tothe sensor interface module 321 illustrated and described in connectionwith FIG. 3 above). For example, a working electrode and a referenceelectrode can each be connected, by separate wires, to a potentiostatpackaged within chip 540. Similarly, the interconnect 534 provides a lowresistance electrical connection between the antenna 536 and thechip-connection pad 538. The interconnect 534 thereby connects theenergy harvesting and communication antenna to electrical componentswithin the chip 540 (e.g., components that function similarly to therectifier module 314 and communication logic 324 illustrated anddescribed in connection with FIG. 3). In some examples, multipleinterconnecting wires can connect terminals (e.g., leads) of the antenna536 to components packaged in the chip 540 (e.g., via respective chipconnection pads).

The chip-connection pads 538, 539 can be formed by a process similar tothe one described above in connection with the interconnects 532, 534and the antenna 536. That is, the chip-connection pads 538, 539 can bepatterned by a photolithography process and metal can be applied byevaporation and/or electroplating to form the chip-connection pads 538,539. The chip-connection pads 538, 539 provide a mounting point for thechip 540 to be flip-chip mounted to the pads 538, 539. Accordingly, thechip-connection pads 538, 539 can be patterned to correspond toterminals of the chip 540. Thus, the arrangement of the chip-connectionpads may vary depending on the packaging of the chip(s) used in theencapsulated electronics structure.

In some examples, one or more of the metal structures patterned onto thefirst layer of bio-compatible material 520 can be a multi-layerarrangement that includes a seed layer (or adhesion layer) patterneddirectly on the bio-compatible material 520. Such a seed layer can beused to adhere to both the bio-compatible material and the bulk of themetal structure that is patterned over the seed layer. For example, sucha seed layer may be a material that adheres well to the bio-compatiblematerial, and also serves as a guide to electroplate the remainder ofthe metal structure.

FIG. 5D illustrates a chip 540 mounted to the connection pads 538, 539.Chip 540 could include, for example, one or more integrated circuits(ICs) and/or one or more discrete electronic components. Anisotropicconductive adhesive 542 is applied to the connection pads 538, 539 tofacilitate electrical and mechanical connection between the connectionpads 538, 539 and corresponding electrodes on the chip 540. Theanisotropic conductive adhesive 542 can include an anisotropicconductive film and/or anisotropic conductive paste that is coated onthe connection pads 538, 539 by deposition, lithography, etc. The chip540 can then be flip-chip mounted to the connection pads 538, 539 bypositioning the chip 540 with its terminals aligned over the respectiveconnection pads (e.g., the connection pads 538, 539). Once aligned, thechip 540 can be urged toward the connection pads 538, 539 to contact theanisotropic conductive adhesive 542 coating, which adheres to theterminals on the chip 540. The anisotropic conductive adhesive 542 bothmechanically adheres the chip 540 to the chip-connection pads 538, 539and electrically connects the chip 540 to the chip-connection pads 538,539 (and thus, to the various electrical components connected throughthe interconnects 532, 534). In some examples, the chip 540 may bemounted to the chip-connection pads 538, 539 using another conductivematerial such as solder, solder paste, and/or conductive epoxy inaddition to, or as an alternative to, the layer of anisotropicconductive adhesive 542.

In some examples, the connection pads 538, 539 may include a soldercoating to facilitate electrical and mechanical mounting of the chip540. For example, while the chip is positioned over the chip-connectionpads, the arrangement can be heated to cause the solder to flow andadhere to the terminals of the chip. In some instances, capillary forcesof the flowing solder may be used to provide a final fine alignment ofthe chip 540. Such a solder coating may be used in addition to, or as analternative to, the anisotropic conductive adhesive 542.

While not specifically shown in FIGS. 5C and 5D, some fabricationprocesses may include forming a reagent layer over the sensor electrodes530. The reagent layer may include a substance used to sensitize thesensor electrodes to a particular analyte. For example a layer includingglucose oxidase may be applied over the sensor electrodes 530 fordetection of glucose.

FIG. 5E illustrates a second layer of bio-compatible material 550 formedover the assembled electronics (i.e., the chip 540 and the patternedconductive material forming wires, electrodes, etc.). The second layerof bio-compatible material 550 functions similar to the first layer ofbio-compatible material 520 to create a bio-compatible exterior surfaceand also electrically isolate the electronics from the surroundingenvironment. In addition, the second layer of bio-compatible material550 structurally supports the assembled electronics and holds thevarious components in place. The second layer of bio-compatible material550 can stabilize the chip 540 by surrounding the chip 540 to fill gapssurrounding the chip 540 (and thereby prevent movement of the chip). Insome examples, the deposition of the second layer of bio-compatiblematerial 550 results in a conformal coating over the assembledelectronics, as illustrated schematically in FIG. 5E. The second layerof bio-compatible material 550 can have a thickness of about 1micrometer to about 50 micrometers, for example.

The second layer of bio-compatible material 550 can be formed of thesame or substantially similar material to the first layer ofbio-compatible material 520 or can optionally be a different polymericmaterial that is both bio-compatible and electrically insulating.

The second layer of bio-compatible material 550 is preferably depositedto create a continuous layer that spans the entirety of the assembledelectronics (i.e., the chip 540 and the patterned conductive materialforming wires, electrodes, etc.). The second layer of bio-compatiblematerial 550 can span a region that extends beyond a footprint of theassembled electronics. As a result, the assembled electronics can besurrounded by portions of the second layer of bio-compatible material550 that rest directly on the first layer of bio-compatible material520. The schematic illustration in FIG. 5D represents such side edges bythe side edge 552 that directly contacts the first layer ofbio-compatible material 520 on one side of the sensor electrodes 530 andby the side edge 554 that directly contacts the first layer ofbio-compatible material 520 on one side of the antenna 536. The secondlayer of bio-compatible material 550 can be a substantially continuous,conformal coating over the assembled electronics between the twocoatings 552, 554.

FIG. 5F illustrates the sealed encapsulating layer 560 formed byannealing together the first layer 520 and second layer 550 of thebio-compatible material. The two layers 520, 550 can be annealedtogether by placing the entire assembled structure, including theworking substrate 502, in an oven at a temperature sufficient to annealthe bio-compatible material in the first and second layers 520, 550. Forexample, parylene C (e.g., dichlorodi-p-xylylene) can be annealedtogether at a temperature of approximately 150 to 200 degrees Celsius.Other bio-compatible polymeric materials (such as PET, PDMS, etc.) mayrequire higher or lower annealing temperatures.

The annealing process causes regions where the first and second layersare in direct contact, such as at the side edges 552, 554 to flow andseal together. Once cooled, the resulting sealed encapsulating layer 560is a continuous layer of bio-compatible material that completelyencapsulates the assembled electronics within. In particular, followingthe annealing process, the boundaries between the first and secondlayers at the side edges 552, 554 are replaced with sealed regions 562,564 where the former edges are annealed together to completely seal theelectronics from the surrounding environment.

During the annealing process, the sacrificial layer 510 separates thebio-compatible material (e.g., the first layer of bio-compatiblematerial 520) from the working substrate 502. Thus, the sacrificiallayer 510 can prevent the bio-compatible material from adhering to theworking substrate 502 during the annealing process.

Alternatively, the sacrificial layer 510 may be omitted (e.g., where thefirst layer of bio-compatible material 520 is formed directly on theworking substrate 502). Thus, the sealed encapsulating layer 560 maydirectly contact the working substrate 502. In such an example, theencapsulated electronics structure can be peeled away from the workingsubstrate 502 following the annealing process. The encapsulatedelectronics structure may also be etched to remove excess bio-compatiblematerial prior to peeling away the structure. For example,bio-compatible material may at least partially wrap around the workingsubstrate 502 either during the deposition process or the annealingprocess or both. Etching (e.g., with an oxygen plasma) can be used tocut away portions of the bio-compatible material that wrap around theworking substrate 502 and also can be used to create a desired shape forthe encapsulated electronics structure. In some examples, theencapsulated electronics structure can be peeled away from the workingsubstrate 502 following such an etching process.

FIG. 5G illustrates an example sensor-revealed encapsulating layer 560′.The sensor-revealed encapsulating layer 560′ may be formed by removing aregion of the encapsulating bio-compatible material to reveal the sensorelectrodes 530. Accordingly, the sensor-revealed encapsulating layer560′ includes an opening 562 in the bio-compatible material on the sideopposite the working substrate 502 (e.g., on the side of theencapsulating bio-compatible layer formed by the second layer ofbio-compatible material 550). The opening 562 can be formed by removingthe region of the bio-compatible material that covers the sensorelectrodes 530. The region of bio-compatible material may be removed bytreating the region with oxygen plasma, for example.

In some embodiments, the opening 562 that reveals the sensor electrodes530 is formed by removing material from the side of the bio-compatiblematerial that is used to cover the assembled electronics, and not fromthe side of the bio-compatible material that is used as a substrate onwhich to assemble the electronics. In this way, the substrate on whichthe electronics are assembled (and thus the substrate the electronicsare initially mounted to) may be left undisturbed while still allowingthe sensor electrodes 530 to be revealed via the opening 562.

In operation, the opening 562 increases the sensitivity of theelectrochemical analyte sensor, particularly for analytes that do notreadily diffuse through the bio-compatible material. By including theopening 562, analyte concentrations can be measured at the sensorelectrodes 530 without diffusing through the bio-compatible material.Thus, when the analyte of interest does not readily diffuse through thelayer of bio-compatible material, the opening 562 allows the analyte toreach the sensor electrodes 530 without passing through theencapsulating bio-compatible material.

FIG. 5H illustrates an example released encapsulated electronicsstructure 570. The released encapsulated electronics structure 570 isreleased from the working substrate 502 by removing the sacrificiallayer 510. For example, if the sacrificial layer is a photoresist, thephotoresist may be rinsed with a rinsing agent such as acetone,isopropyl alcohol, etc. If the sacrificial layer is a soap film, watermay be used to rinse away the soap and release the encapsulatedelectronics structure 570. Such a rinsing agent may be configured toremove the sacrificial layer 510 without also degrading thebio-compatible material.

The released encapsulated electronics structure 570 is suitable forbeing incorporated into a biological environment, such as within aneye-mountable device or an implantable medical device, for example. Dueto the encapsulating bio-compatible material, the surroundingenvironment is sealed from the encapsulated electronics. For example, ifthe structure is implanted in a biological host, or placed in aneye-mountable device to be exposed to tear fluid (e.g., similar to thesubstrate 230 discussed in connection with FIG. 2 above), the structureis able to be exposed to fluids of the biological host (e.g., tearfluid, blood, etc.), because the entire exterior surface is coated withbio-compatible material that lacks gaps or seams.

In some instances, an additional etching process may be performed priorto releasing the encapsulated electronics structure 570. For example,excess bio-compatible material may be trimmed away from the encapsulatedstructure by etching the excess material. Additionally or alternatively,the completed encapsulated structure can be separated from neighboringencapsulated structures assembled in parallel on the same workingsubstrate by etching through overlapping regions of annealedbio-compatible material that connect neighboring structures. An oxygenplasma etching process can be used to cut out the encapsulated structurein a desired shape prior to releasing the encapsulated structure. Insome examples, the encapsulating bio-compatible material can be etchedin the shape of a flattened ring similar to the shape of the substrate230 illustrated and described in connection with FIG. 2 above, forexample.

In some examples, the etching that shapes the encapsulated structure 570into a ring-shaped structure can also be used to form the opening 562over the sensor electrodes 530. For example, the bio-compatible materialcan be a material that is readily removed by oxygen plasma. The oxygenplasma can then be used to form encapsulated structure 570 into adesired shape, such as a ring shape, by directing the oxygen plasma overportions of the bio-compatible material. In contrast, the sensorelectrodes 530 can be formed of a material that is not readily etched bythe oxygen plasma, so that the sensor electrodes 530 can function as anetch stop. To form the opening 562, the oxygen plasma can remove thebio-compatible material covering the sensor electrodes 530 while leavingthe sensor electrodes 530 substantially intact.

Additionally or alternatively, the encapsulated electronics structure570 may be released from the working substrate 502 by peeling theencapsulated electronics structure 570 away from the working substrate502. For instance, in an example where the sacrificial layer 510 isomitted, the encapsulated electronics structure 570 may be formeddirectly on the working substrate 502. The encapsulated electronicsstructure 570 may be etched to create a ring-shaped structure (oranother desired shape for the encapsulated electronics structure) andthe encapsulated electronics structure can then be peeled away from theworking substrate 502.

The description in FIGS. 5A through 5H describes one example of anassembly process for creating an encapsulated electronics structuresuitable for being mounted within an eye-mountable device. For example,the cross-sectional views shown in FIGS. 5A through 5H can be a slicethrough a flattened ring similar to the flattened-ring-shaped substrate230 shown and described in connection with FIG. 2 above. In suchexamples, the encapsulated electronics structure 570 may be mountedwithin an eye-mountable device, such as within a polymeric material(e.g., a hydrogel material) formed to be contact-mounted to a cornealsurface. The electrochemical sensor can then be used to measure theanalyte concentration of tear film that absorbs into the polymericmaterial of the eye-mountable device. However, a similar process can beemployed to create bio-compatible encapsulated electronics for otherapplications. For example, implantable electronic medical devices may becreated by assembling electronics on a first layer of a bio-compatiblematerial, a second layer of bio-compatible material can be formed overthe electronics, and the two layers can be annealed together to fullyencapsulate the electronics within the bio-compatible material. Such animplantable electronic medical device may be formed on a workingsubstrate coated with a sacrificial layer, and may be released from theworking substrate by rinsing the sacrificial layer. Such implantableelectronic medical devices may include an antenna for communicatinginformation (e.g., sensor results) and/or inductively harvesting energy(e.g., radio frequency radiation). Implantable electronic medicaldevices may also include electrochemical sensors or they may includeother electronic devices.

Some embodiments of the present disclosure relate to an encapsulatedelectronics structure that includes an electrochemical sensor. Forexample, a chip connected to sensor electrodes an antenna (e.g., thechip 540 connected to the sensor electrodes 530 and antenna 536) can beconfigured to apply a voltage across the sensor electrodes, measure anamperometric current through the working electrode, and wirelesslycommunicate the measured amperometric current with the antenna. In someexamples a dedicated module, such as integrated circuit with suitableprogram logic, interfaces, etc., is packaged in a single chip (e.g., thechip 540), however the functions described above can be carried out byany combination of hardware and/or software implemented modules. Thus,some embodiments of the present disclosure that relate toelectrochemical sensors refer to encapsulated electronics that includean antenna and a controller, where the controller is a module configuredto carry out one or more of the functions described above.

It is noted, however, that the present disclosure may includeelectronics modules that are configured to perform functions in additionto, or as alternatives to, those described above. For example, theencapsulated electronics module may include a light sensor, temperaturesensor, and/or other sensors useful for detecting diagnosticallyrelevant information in an ophthalmic and/or implantable application.The encapsulated electronics module may, for example, obtain atemperature reading and then communicate the temperature information oruse the temperature information to modify a measurement procedure withthe electrochemical sensor. Moreover, the encapsulated electronicsmodule can include a combination of capacitors, switches, etc., toregulate voltage levels and/or control connections with otherelectronics modules. For example, the encapsulated electronics modulemay include a capacitor for regulating a voltage supply generated byharvesting energy from the antenna, similar to the capacitor 316described in connection with FIG. 3 above. Thus, some embodiments of theencapsulated electronics module (e.g., the controller and/or antenna)may include a variety of circuit-design and other modifications toachieve functions desired for a particular implementation.

FIG. 6A is a flowchart of an example process 600 for producing anencapsulated electronics module. A sacrificial layer is formed on aworking substrate (602). The sacrificial layer can be a photoresist, asilane, a non-stick coating, such as a soap film, etc. A first layer ofbio-compatible material is formed on the sacrificial layer (604). Thefirst layer of bio-compatible material can include a polymeric materialsuch as parylene C (e.g., dichlorodi-p-xylylene), a polyethyleneterephthalate (PET), a polydimethysiloxane (PDMS), other siliconeelastomers, and/or another bio-compatible polymeric material. The firstlayer of bio-comaptible material can be formed by a microfabricationprocess such as deposition, etc. In some examples, the first layer ofbio-compatible material is formed with a substantially uniform thicknesssuch that the exposed side of the bio-compatible material (i.e., theside opposite the working substrate) is a substantially flat surfacethat can be used as a substrate for assembling electronics.

An electronics module is provided on the exposed side of the first layerof bio-compatible material (606). The electronics module can beassembled as described above, for example, in connection with FIGS. 5Cand 5D. Thus, the first layer of bio-compatible material can be used asa substrate for assembly of the electronics module thereon.Alternatively, the electronics module could be placed on the first layerof bio-compatible material in a fully or partially assembled form. Theelectronics module can include patterned metal arranged as wires,electrodes, connection pads, antenna(e), etc. Microfabricationtechniques such as photolithography, evaporation, electroplating, etc.can be used to pattern metal in an arrangement suitable for theelectronics module. The electronics module can also include one or moreintegrated circuits, which may be flip chip mounted. In some examplesanisotropic conductive adhesive may be used to electrically andmechanically connect terminals of a packaged integrated circuit tocorresponding connection pads.

A second layer of bio-compatible material is formed over the assembledelectronics module (608). The second layer of bio-compatible materialmay be a bio-compatible polymeric material that is the same as the firstlayer of bio-compatible material. The second layer may be formed via amicrofabrication technique, such as evaporation, to create a conformallayer over the assembled electronics, and that overlaps the entirety ofthe assembled electronics such that outer edges of the second layer ofbio-compatible material directly contacts the first layer ofbio-compatible material. The two layers of bio-compatible material canthen be annealed together (610). The annealing process can seal the twolayers of bio-compatible material together and thereby encapsulate theassembled electronics within the bio-compatible material.

In some examples, the first layer of bio-compatible material can beformed directly on the working substrate, rather than on the sacrificiallayer. For example, a layer of material such as parylene C can be formeddirectly on a clean silicon wafer. Once a second layer of bio-compatiblematerial is annealed to the first layer so as to encapsulate theelectronics module, the encapsulated structure can be peeled away fromthe working substrate. Thus, the sacrificial layer may be omitted fromthe assembly process. That is, in some embodiments, the process 600described in the flowchart of FIG. 6A may omit block 602.

FIG. 6B is a flowchart of an example process 620 for incorporating anencapsulated electronics module into an eye-mountable device. Theencapsulated electronics module can be etched to remove a region of thebio-compatible material and thereby reveal sensor electrodes (622).Thus, block 622 applies to examples where the encapsulated electronicsinclude an electrochemical sensor with sensor electrodes, and may beomitted if the encapsulated electronics include other bio-interactiveelectronics. The region can be removed by etching the bio-compatiblematerial with an oxygen plasma, for example. The region ofbio-compatible material that is removed may be from the layer ofbio-compatible material applied to cover the assembled electronics(e.g., the layer discussed in connection with block 608), rather thanthe layer applied over the sacrificial layer to create a substrate forassembling the electronics (e.g., the layer discussed in connection withblock 604). The electronics modules are initially mounted to the layerof bio-compatible material used as a substrate for assembling theelectronics, which is referred to herein for convenience only as the“substrate layer”. By leaving the substrate layer of bio-compatiblematerial undisturbed while revealing the sensor electrodes, theinitially formed bond between the sensor electrodes and the substratelayer remains intact. Revealing the sensor electrodes without disturbingthe initial mounting bonds results in an assembled device that benefitsfrom the structural integrity and resiliency of the initial mountingbonds between the sensor electrodes and the substrate layer ofbio-compatible material.

The assembled encapsulated structure can be etched to create aring-shaped structure (624). For example, the encapsulated structure maybe etched to create a flattened-ring-shape similar to the ring-shapedsubstrate 230 shown and described in connection with FIG. 2 above. Theencapsulated structure may also be etched in another shape, such as arectangle, a circle (e.g., a disc), an oval, etc. to create a generallyflat structure in which assembled electronics are encapsulated by sealedbio-compatible material. In some examples, the etching process of block624 includes cutting through the areas where the two layers ofbio-compatible material are annealed together (e.g., as discussed inblock 612). Thus, the etching process of block 624 may include cuttingthrough the sealed edges of bio-compatible material that surround theencapsulated electronics. In some examples, the two layers ofbio-compatible material (and the working substrate and sacrificiallayer) can span a plurality of assembled electronics modules. Forexample, the working substrate may be divided into a grid, with eachunit occupied by an assembled electronics module, and the sacrificiallayer and layers of bio-compatible material can be extended across theentire grid in a substantially continuous manner. In such an example,the etching process of block 624 may thus be used to separate thedistinct electronics modules from one another by cutting through theannealed bio-compatible material that extends between the separatemodules. Following block 624, the resulting encapsulated electronicsstructure is shaped to be integrated into a biological host environment,such as in an eye-mountable device, an implantable medical device, etc.

The sacrificial layer is removed to release the encapsulated structurefrom the working substrate (626). The sacrificial layer can be removedby applying a rinsing agent to dissolve the sacrificial layer. Forexample, acetone or isopropyl alcohol can be applied to dissolve thesacrificial layer and thereby release the encapsulated structure. Therinsing agent is selected to react with the sacrificial layer (e.g., bydissolving), but not react with the bio-compatible material thatencapsulates the assembled electronics. In an example with soap filmused as the sacrificial layer, water can be used to rinse away the soapfilm.

The released encapsulated structure can then be embedded into polymericmaterial of an eye-mountable device (628). Where the encapsulatedstructure is given a flattened-ring shape (i.e., during the etchingprocessing block 624), the structure can be embedded around theperipheral region of a generally circular polymeric material shaped tobe contact-mounted to an eye. Such a polymeric material may have, forexample, a concave surface configured to be mounted over a cornealsurface of an eye and a convex surface opposite the concave surfaceconfigured to be compatible with eyelid motion while mounted to thecorneal surface. For example, a hydrogel material (or other polymericmaterial) can be formed around the encapsulated structure in aninjection molding process.

FIG. 7 depicts a computer-readable medium configured according to anexample embodiment. In example embodiments, the example system caninclude one or more processors, one or more forms of memory, one or moreinput devices/interfaces, one or more output devices/interfaces, andmachine-readable instructions that when executed by the one or moreprocessors cause the system to carry out the various functions, tasks,capabilities, etc., described above.

As noted above, in some embodiments, the disclosed techniques can beimplemented by computer program instructions encoded on a non-transitorycomputer-readable storage media in a machine-readable format, or onother non-transitory media or articles of manufacture. FIG. 7 is aschematic illustrating a conceptual partial view of an example computerprogram product that includes a computer program for executing acomputer process on a computing device, arranged according to at leastsome embodiments presented herein, including the processes shown anddescribed in connection with FIGS. 6A and 6B.

In one embodiment, the example computer program product 700 is providedusing a signal bearing medium 702. The signal bearing medium 702 mayinclude one or more programming instructions 704 that, when executed byone or more processors may provide functionality or portions of thefunctionality described above with respect to FIGS. 1-6. In someexamples, the signal bearing medium 702 can include a non-transitorycomputer-readable medium 706, such as, but not limited to, a hard diskdrive, a Compact Disc (CD), a Digital Video Disk (DVD), a digital tape,memory, etc. In some implementations, the signal bearing medium 702 canbe a computer recordable medium 708, such as, but not limited to,memory, read/write (R/W) CDs, R/W DVDs, etc. In some implementations,the signal bearing medium 702 can be a communications medium 710, suchas, but not limited to, a digital and/or an analog communication medium(e.g., a fiber optic cable, a waveguide, a wired communications link, awireless communication link, etc.). Thus, for example, the signalbearing medium 702 can be conveyed by a wireless form of thecommunications medium 710.

The one or more programming instructions 704 can be, for example,computer executable and/or logic implemented instructions. In someexamples, a computing device is configured to provide variousoperations, functions, or actions in response to the programminginstructions 704 conveyed to the computing device by one or more of thecomputer readable medium 706, the computer recordable medium 708, and/orthe communications medium 710.

The non-transitory computer readable medium 706 can also be distributedamong multiple data storage elements, which could be remotely locatedfrom each other. The computing device that executes some or all of thestored instructions can be a microfabrication controller, or anothercomputing platform. Alternatively, the computing device that executessome or all of the stored instructions could be remotely locatedcomputer system, such as a server.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments will be apparent to those skilled in the art.The various aspects and embodiments disclosed herein are for purposes ofillustration and are not intended to be limiting, with the true scopebeing indicated by the following claims.

1-20. (canceled)
 21. An eye-mountable device comprising: a transparentpolymeric material having a concave surface and a convex surface,wherein the concave surface is configured to be mounted over a cornealsurface and the convex surface is configured to be compatible witheyelid motion when the concave surface is so mounted; a liquid crystalmaterial embedded within the transparent polymeric material; aring-shaped structure embedded in the polymeric material, wherein thering-shaped structure comprises electronic components encapsulatedwithin a bio-compatible material, wherein the bio-compatible materialincludes a first layer and a second layer in which the electroniccomponents are interposed between the first and second layers, whereinthe electronic components include an antenna, a light sensor, and acontroller, wherein the controller is coupled to the antenna, the lightsensor, and the liquid crystal material.
 22. The eye-mountable device ofclaim 21, wherein the controller is configured to engage in wirelesscommunication via the antenna.
 23. The eye-mountable device of claim 21,wherein the controller is configured to harvest energy from radiofrequency radiation received by the antenna.
 24. The eye-mountabledevice of claim 21, wherein the electronic components further includeone or more light sources coupled to the controller.
 25. Theeye-mountable device of claim 21, wherein the controller comprises anintegrated circuit.
 26. The eye-mountable device of claim 21, whereinthe antenna comprises a loop of conductive material.
 27. Theeye-mountable device of claim 21, wherein portions of the first andsecond layers are annealed together.
 28. The eye-mountable device ofclaim 21, wherein the ring-shaped structure includes a conductor that isnot encapsulated within the bio-compatible material.
 29. Theeye-mountable device of claim 21, wherein the bio-compatible materialcomprises a dichlorodi-p-xylylene polymer.